The present invention relates to forming oxide and silicon layers within a single semiconductor processing chamber, and more particularly to thermal oxidation within a single-wafer epitaxial silicon deposition chamber.
High-temperature ovens, called reactors, are used to create structures of very fine dimensions, such as integrated circuits on semiconductor substrates. One or more substrates, such as silicon wafers, are placed on a wafer support inside the reaction chamber. Both the wafer and support are heated to a desired temperature. In a typical wafer treatment step, reactant gases are passed over the heated wafer, causing the chemical vapor deposition (CVD) of a thin layer of the reactant material on the wafer. Various process conditions, particularly temperature uniformity and reactant gas distribution, must be carefully controlled to ensure the high quality of the resulting layers.
Through a series of deposition, doping, photolithography and etch steps, the starting substrate and the subsequent layers are converted into integrated circuits, with a single layer producing from tens to thousands or even millions of integrated devices, depending on the size of the wafer and the complexity of the circuits.
Batch processors have traditionally been employed in the semiconductor industry to allow multiple wafers to be processed simultaneously, thus economically presenting low processing times and costs per wafer. Recent advances in miniaturization and attendant circuit density, however, have lowered tolerances for imperfections in semiconductor processing. Accordingly, single wafer processing reactors have been developed for improved control of deposition conditions.
Among other process parameters, single wafer processing has greatly improved temperature and gas flow distribution across the wafer. In exchange for greater process control, however, processing time has become even more critical than with batch systems. Every second added to processing times must be multiplied by the number of wafers being processed serially, one at a time, through the same single-wafer processing chamber. Conversely, any improvements in wafer throughput can translate to significant fabrication cost savings.
One process for which process control is particularly critical, and for which single wafer processing is particularly useful, is the formation of epitaxial layers. If the deposited layer has the same crystallographic structure as the underlying silicon wafer, it is called an epitaxial layer. Through careful control of deposition conditions, reactant gases are passed over a heated substrate such that the deposited species precipitates in conformity with the underlying crystal structure, which is thus extended into the growing layer. As is known in the art, epitaxial layers can be formed of intrinsic or doped silicon, silicon germanium, or other semiconductor materials. The lowest level of devices, including transistors, are often formed within an epitaxial layer formed over a semiconductor substrate.
Because integrated devices are formed within the epitaxial layer, it is important that the epitaxial layer maintain a pure crystal structure, free of contamination which could affect device operation. The purity and crystalline structure of the underlying substrate (or other base layer) prior to epitaxial deposition is one factor affecting the resultant epitaxial layer. Contaminants at the substrate surface can interfere with the crystal structure of the epitaxial layer, or with the electrical properties of devices made out of the epitaxial layer. Similarly, crystal dislocations in the underlying layer are propagated through the growing epitaxial layer. Of course, contamination of the epitaxial layer after formation can also critically affect electrical characteristics of the devices formed therein.
A need exists, therefore, for methods of purifying substrate surfaces prior to chemical vapor deposition, and of maintaining the purity of a deposited layer after formation. Desirably, such methods should be compatible with single-wafer, epitaxial silicon deposition chambers without increasing system costs or reducing wafer throughput.
These and other needs are satisfied by several aspects of the present invention.
In accordance with one aspect of the present invention, an atmospheric silicon deposition reactor includes a single-substrate reaction chamber. A reaction gas inlet and an outlet of the chamber define a gas flow path between them. A support is included for supporting a substrate within the gas flow path. The reactor includes a source of hydrogen gas suitable for flowing through the reaction chamber as a carrier gas during epitaxial silicon deposition, a source of silicon-containing gas, and a source of a gaseous oxidizing agent suitable for thermal growth of silicon dioxide from a silicon layer. Gas lines connect the sources of gases to the reaction chamber.
In accordance with another aspect of the invention, a chemical vapor deposition reactor includes a process chamber with a gas inlet and a gas outlet. A first gas line communicates hydrogen gas between a hydrogen container and the gas inlet. A second gas line communicates a mixture of O2 and a non-reactive gas between an oxidant source container and the gas inlet. The level of oxygen in oxidant source container is non-explosive in the presence of any amount of hydrogen under operating conditions of the process chamber.
In accordance with another aspect of the invention, a method of processing semiconductor substrates includes forming an epitaxial layer containing silicon in a chemical vapor deposition chamber and forming an oxide layer over the epitaxial layer within the chamber.
In accordance with another aspect of the invention, a method of fabricating integrated circuits on a semiconductor substrate includes loading the substrate into a chemical vapor deposition processing chamber. An epitaxial silicon layer is deposited on at least part of the substrate within the chamber. A thermal oxide layer is grown over the epitaxial silicon layer within the chamber, and a polysilicon layer is deposited over the thermal oxide layer, also within the chamber.
In accordance with another aspect of the invention, a method of processing a semiconductor substrate includes loading the substrate into a chemical vapor deposition chamber. An oxidant source gas including O2 is introduced into the chamber, and an oxide is grown from a silicon surface of the substrate. The flow of the oxidant source gas is shut off, and the oxidant source gas purged from the chamber with a gas containing hydrogen.
In accordance with another aspect of the invention, a method of forming layers over a semiconductor substrate in a single substrate reactor includes loading the substrate into a single-substrate reaction chamber. An oxide layer is grown over the substrate, within the reaction chamber at about atmospheric pressure, by exposing a top surface of the substrate to an oxidant. A silicon layer is deposited, within the reaction chamber at about atmospheric pressure, directly on the oxide layer.